Floating pistons

ABSTRACT

The piston is of metal reinforced elastomeric material of substantially cup-shaped configuration having its base of a thickness resilient to ballooning or excessive flexure under pressure, and being of a diameter slightly greater than the internal diameter of the cylinder in which it moves. The base having true cylindrical marginal bearing surfaces bounded by sharply angular axial edges and constituting only a relatively small portion of the total height of the piston. The greater portion of the axial extent of the piston is comprised by an annular flange portion of only slightly less diameter than that of the cylinder, the flange portion serving as a guiding means for installing the piston and being reinforced by a tubular metal piece which also abuts a portion of the base of the piston.

waited States Patent 91 DeCarhon 11] avaaasa 1 May1,1973

[ FLOATING PISTONS Christian Bourcier DeCarbon, 64 Boulevard MauriceBarres, Neuillysur-Seine, France 22 Filed: I Oct. 26, 1970 21 Appl. No.:83,708

[76] inventor:

51 int. C1. ..Fl6j 1/00 [58] Field of Search ..92/248, 249, 245, 92/241,254, 240; 267/64; 138/31; 277/212 C [56] References Cited UNITED STATESPATENTS "La Lb Primary Examiner-Irwin C. Cohen I AssistantExaminer-Irwin C. Cohen Attorney-Watson, Cole, Grindle & Watson 5 7]ABSTRACT The piston is of metal reinforced elastomeric material ofsubstantially cup-shaped configuration having its base of a thicknessresilient to ballooning or excessive flexure under pressure, and beingof a diameter slightly greater than the internal diameter of thecylinder in which it moves. The base having true cylindrical marginalbearing surfaces bounded by sharply angular axial edges and constitutingonly a relatively small portion of the total height of the piston. Thegreater portion of the axial extent of the piston is comprised by anannular flange portion of only slightly less diameter than that of thecylinder, the flange portion serving as a guiding means for installingthe piston and being reinforced by a tubular metal piece which alsoabuts a portion of the base of the piston.

2 Claims, 5 Drawing Figures FLOATENG PISTONS The present inventionrelates to improvements made in floating pistons used as separatorsbetween two fluids such as two liquids or a liquid and a gas, saidseparators having to move inside cylinders under the effect of adifference in pressure on both sides of their faces. It applies moreparticularly to separators used in oleopneumatic monotube shockabsorbers.

The difficulty in making pieces of this type lies in the choice of asystem that combines good fluid tightness in both directions with a goodlubrication of the rubbing part assuring the fluid tightness and whichmust be guided in the cylinder in a satisfactory way to obtain a gentlesliding and consequently a slight wear and limited differences inpressure in functioning. Further, diffusion of the gas through thefloating piston has to be avoided.

Floating pistons intended to meet these needs are already known throughFrench Pat. No. 1,055,443 of May 5, 1952 and U.S. Pat. No. 3,269,718 ofAug. 30, 1966.

These two inventions which already constituted important progress inrelation to existing solutions, still have a certain number ofimperfections. Actually, the flexible piston, shown in FIG. 3 of FrenchPat. No. 1,055,443 does not comprise a metal reinforcement. so thatthere is no guiding during sliding. Further, an uncontrolledinterference of the deformation of the flexible base with the zone offluid tightness occurs.

On the contrary, the flexible piston of U.S. Pat. No. 3,269,718comprises a metal reinforcement which as sures stability, but it doesnot directly assure guiding.

This function is assured by two fluid tightness beads with a toricsurface.

Practice has shown, however, that a toric fluid tight surface assures aless good fluid tightness and presents a more rapid wear than acylindrical fluid tight surface.

Another drawback of this arrangement is made up by the large surface andthe slight thickness of the deformable membrane which leads to a quiterapid diffusion of the gas contained in the chamber.

Also, in the case of this patent there is an imbalance between theelasticity of the membrane, on the one hand, and the sliding force ofthe piston, on the other hand.

An effort has been made to find a satisfactory solution to theseproblems by making a floating piston such as shown in FIG. 1 of thepresent application. As can be seen from this drawing, the floatingpiston is made up of a reinforcement in the shape of a cup 3 covered onthe outside with rubber 2 or the like. However, this embodiment is nolonger satisfactory, because either fitting can be given to the pistonin cylinder 1 so that it will move easily, then the fluid tightness ispoor, or else, sufficient tight fitting is given to obtain a perfectfluid tightness, but then there is too much friction between rubber 2and cylinder 1 and the piston moves with difficulty. Actually,lubricating the rubbing surfaces is very bad because of too much tightfitting, all the more so in this case since the rubber has a tendency toadhere to the surface of cylinder 1 by a sticking action.

The present invention aims at preventing these drawbacks, and has forits object improvements made in floating pistons used as separatorsbetween two fluids such as a gas and a liquid, particularly inoleopneumatic monotube shock absorbers, said shock absorbers movinginside cylinders under the action of a pressure difference, saidseparators being made up of an element of rubber or the like combinedwith a metal reinforcement, characterized by the fact that the floatingpiston comprises at least a fluid tightness bead, each extending over aslight part of the axial height of said piston, the fluid tightness beador beads being one piece with the rubber parts of the piston and havinga greater diameter than that of the cylinder in which they slide so thatit is subjected to a certain tight fitting when it is mounted in thecylinder, the metal reinforcement being arranged so that in relation tothe fluid tightness beads it assures directly or indirectly the guidingof said piston.

In developing this general inventive idea, it is provided:

that several fluid tightness beads are arranged regularly spaced on theoutside surface of the piston, separated by circumferential grooves,said grooves possible being filled with a lubricant;

that the piston comprises a cylindrical part adjusted with a slight playor very slight tight fitting in the cylinder assuring the guiding ofsaid piston in the cylinder and that it comprises a fluid tightness beadextending over a slight part of the axial height of said piston;

that the fluid tightness bead has a cylindrical outside surface,delimited by sharp angles;

that the metal reinforcement is buried in the rubber I of the piston andthat is has the shape of a cylinder opened at both ends, one of the endsbeing closed by the bottom of the floating piston of rubber or the like;

that the metal reinforcement is cylindrical and constitutes the guidingpart of the floating piston, the reinforcement being preferably made ofaluminum alloy and arranged around an element of rubber or the likecomprising a fluid tightness bead and the bottom of the floating piston;and

that the metal reinforcement is in the shape of a cup and that at leastthe fluid tightness bead is made of rubber or the like covering asurface corresponding to said cup.

By way of example and to make understanding of the following descriptioneasier, there are represented on the accompanying drawings:

FIG. 1 a lengthwise section of an embodiment of the floating piston thatis not satisfactory.

FIG. 2, a lengthwise section according to a first embodiment of theinvention.

FIG. 3, a lengthwise section of a variant according to a secondembodiment.

FIG. 4, a lengthwise section according to a third embodiment.

'FIG. 5, a lengthwise section according to a fourth embodiment.

Referring to these figures, it can be seen that cylinder 1 containsfloating piston 2 of rubber or any other material presenting a suitableelasticity, a good resistance to fluids present. A metal reinforcement3, preferably of steel, is inserted during molding of the rubber. Thisreinforcement 3 can present a reversed L section 3a as shown in FIG. 2,leading to good resistance to deformations. It can, nevertheless,present any other shape, in particular, it can be cylindrical. The unitassures isolation of areas A and B.

Rubber element 2 presents four distinct zones:

"between zone 2a forming the base of zone 2a forming the base offloating piston 2;

zone 2b mounted with tight fitting in cylinder 1 assuring fluidtightness and presenting an outside surface that is preferablycylindrical but able to have any other profile;

zone 20 assuring the guiding, by using the good rubber qualities of therubber on the steel in the presence of oil, this zone 20 sliding incylinder 1 with a slight play or a very slight tight fitting;

zone 2d forming an annular flange or heel portion assures a good seatingor guiding of the floating piston during emplacement.

Metal reinforcement 3 is intended to give a good stabilityto theassembly and to control the interferences piston 2 and the zone 2bassuring fluid tightness.

In FIG. 3, the floating piston presents the same general shape, butreinforcement 3 here is outside rubber element 2.

In this case, reinforcement 3' directly assures the guiding and ispreferably made of aluminum alloy. Reinforcement 3' is put in placeeither after molding of the rubber or during the molding operation.

When pressure difference occurs between areas A and B, the base or zone2a is slightly deformed in one direction or the other which results inincreasing the fluid tightness during sliding so that the dangers ofleaks are reduced.

The floating piston assembly slides therefore in cylinder 1 guided byzone '20 until the reestablishment of equilibrium. With the designaccording to the invention, an identical sliding force in bothdirections and a deformation of the membrane having a tendency toreinforce the fluid tightness during sliding are obtained.

In the case of FIG. 4, the reinforcement is made up of a cup 3"surrounded on the outside by rubber or the like. In, this case, face 2ais practically undeformed, but the tight fitting in zone 2b is generallysufficient for a good fluid tightness. It should be noted that thissolution is very simple and it is even possible not to cover the bottomof the cup with rubber so that only zones 2b and 2c are covered withrubber.

In FIG. 5, is shown a solution with several fluid tightness beads 2bseparated by circumferential grooves 2'11. Reinforcement 3 is still madeup of a cup covered on the outside surfaces with rubber or the like.Guiding is obtained by fluid tightness beads 2b work ing withreinforcement 3 which is so arranged that in relation to said beads itassures a uniform distribution of the tight fitting and gives a suitablestiffness to the assembly. Grooves 2'd can be filled with lubricant, forexample, grease before mounting.

! claim:

l. A floating piston device for use as a separator between two fluidbodies within a cylinder, such as that of an oleopneumatic shockabsorber, said piston comprising a cup-like structure being constructedof rubber or other elastomeric material and having a closed marginalbearing base portion adapted to extend across the cylinder and of athickness permitting only moderate flexure under pressure from one sideof the piston or the other, and an annular open ended flange portionadapted to extend axially in the cylinder, said base portion being of anaxial height comprising only a slight portion of the total axial heightof the piston and being of a diameter slightly1 greater than that of thecylinder to insure a flu1 g fit; the flange portion of the pistoncomprising the greater portion of the height of the piston being of anoutside diameter slightly less than the internal diameter of the piston,thus insuring proper guidance into the cylinder when the piston isinstalled; said base portion having a purely cylindrical surface withsharp angular edges at both axial terminations; the flange portion ofthe piston being surrounded and engaged by a tubular ring of metal whichabuts said base portion and which serves to reinforce both the guidingflange portion and the marginal bearing portions of the base of thepiston.

2. A piston device as set forth in claim 1 in which the metalreinforcing ring is made of an aluminum alloy.

1. A floating piston device for use as a separator between two fluidbodies within a cylinder, such as that of an oleopneumatic shockabsorber, said piston comprising a cup-like structure being constructedof rubber or other elastomeric material and having a closed marginalbearing base portion adapted to extend across the cylinder and of athickness permitting only moderate flexure under pressure from one sideof the piston or the other, and an annular open ended flange portionadapted to extend axially in the cylinder, said base portion being of anaxial height comprising only a slight portion of the total axial heightof the piston and being of a diameter slightly greater than that of thecylinder to insure a fluid-tight fit; the flange portion of the pistoncomprising the greater portion of the height of the piston being of anoutside diameter slightly less than the internal diameter of the piston,thus insuring proper guidance into the cylinder when the piston isinstalled; said base portion having a purely cylindrical surface withsharp angular edges at both axial terminations; the flange portion ofthe piston being surrounded and engaged by a tubular ring of metal whichabuts said base portion and which serves to reinforce both the guidingflange portion and the marginal bearing pOrtions of the base of thepiston.
 2. A piston device as set forth in claim 1 in which the metalreinforcing ring is made of an aluminum alloy.